Vehicle occupant restraint belt retractors have heretofore been provided with winding prevention mechanisms for selectively relieving the tension on the belt to enhance comfort of the occupant by holding the belt at a slackened length. U.S. Pat. No. 3,869,098 by Raymond G. Sprecher, issued Mar. 4, 1975, discloses a belt retractor in which actuation of the winding prevention feature occurs in response to a predetermined sequence of belt winding and unwinding movement U.S. Pat. No. 4,153,274 by Lloyd W. Rogers, Jr. et al, issued May 8, 1979, provides a winding prevention mechanism which is manually actuated.
It is characteristic of the winding prevention mechanisms of both these patents that the winding prevention feature is cancelled in response to a predetermined extent of belt unwinding so that the winding effort of the windup spring is restored to pull the belt taut about the seated occupant. In a retractor having such a winding prevention mechanism, it is possible for the vehicle occupant to unbuckle the seat belt without having performed the belt unwinding motion necessary to cancel the winding prevention mechanism and the belt will not be retracted onto the reel. U.S. Pat. No. 3,973,786 by Lloyd W. Rogers, Jr. issued Aug. 10, 1976, provides an improvement wherein the winding prevention mechanism is automatically cancelled whenever the door is moved from the closed to the open position.
U.S. Pat. No. 4,285,479 by Hubert P. Blom, issued Aug. 25, 1981, provides a further improvement wherein the winding prevention mechanism is cancelled by an inertia sensor upon the occurrence of a sensed condition of vehicle deceleration so that the belt will be rewound to a taut condition about the occupant. In Blom, a cam member is coupled to a pendulum. Upon occurrence of a predetermined level of deceleration, the pendulum pivots and carries the cam member into engagement with a winding prevention pawl to disengage the pawl from ratchet teeth and thereby release the reel for rotation in the belt winding direction by the windup spring. The aforedescribed inertia release device of the Blom patent required a relatively large inertia weight in order to obtain the level of force required to operate the cam member to disengage the pawl from the ratchet teeth.
It was recognized that it would be desirable to provide an improved release mechanism in which a relatively small inertia weight could trigger the release of the winding prevention mechanism and permit the windup spring to pull the belt taut against the occupant. Accordingly, U.S. Pat. No. 4,540,137 issued Sept. 10, 1985 by Lloyd W. Rogers, Jr. et al provided a further improvement in which a winding prevention pawl is mounted upon a collapsible support mechanism which is collapsed by a relatively small pendulum at the onset of a sensed vehicle deceleration condition so that force imposed on the pawl by the windup spring shifts the pawl against a cam which moves the pawl axially out of engagement with the ratchet teeth carried by the reel so that the windup spring will rewind the belt to a taut condition about the occupant.
A shortcoming of the aforedescribed devices for cancelling the winding prevention mechanism in response to a sensed inertia condition is that it was necessary to add an inertia sensor to the retractor even though retractors of the vehicle sensitive inertia type already have an inertia sensor for locking the retractor against belt unwinding.
It would be desirable to provide an improved release mechanism in which a single inertia sensing pendulum could perform both the functions of cancelling out the winding prevention mechanism so that any slack would be removed from the belt and also locking the retractor against belt unwinding rotation.